Method for reducing the permeability of alloys by hydrogen



Patented Aug. 3, 1954 UNITED STATES 1' OFFICE I METHOD FOR REDUCING THE PERMEA- BILITY F ALLOYS BY HYDROGEN States Atomic Energy Commission No Drawing. Application January 5, 1952, Serial No. 265,207

Claims.

This invention relates to metal containers for holding hydrogen at elevated temperatures and to a method for treating metals to reduce the permeability thereof by hydrogen at elevated temperatures.

It is well known that metals, such as alloy steels, Nichrome, etc., commonly used for hydrogenation equipment and other hydrogen containers, laboratory equipment, etc. are permeable by hydrogen at elevated temperatures resulting in large loss of hydrogen from such equipment. Because of such losses, the determinations of the dissociation temperatures, etc. of many compounds which evolve hydrogen at elevated temperatures have varied greatly and have been unreliable or only approximate.

I have discovered that alloys comprising iron, nickel and chromium, such as stainless steel, etc., when heated at an elevated temperature in contact with hydrogen for a prolonged period of time become gradually less permeable by hydrogen and after prolonged heating in contact with hydrogen for several days their permeability by hydrogen may be reduced one hundrediold or more. The temperature used should not be substantially less than that at which the gas is fully mobile with the metal being treated. In general, this temperature is about 600 C. In the treatment of such alloys I have obtained good results by heating at a temperature between about 600 C. and 900 C. but I prefer to employ a temperature of about 800 C. A higher temperature may be used but usually is not necessary. I have further discovered that the advantageous results thus obtained can be destroyed to a large extent if the heated metal is exposed to air at room temperature and to a greater extent if the treated metal is exposed to air while heated at an elevated temperature. Therefore, in order to preserve the imparted property of low permeability by hydrogen, the treated metal or the treated fabricated article or at least one surface thereof should be kept in an environment free of oxygen, such for example as hydrogen, argon or other monatomic gas.

, The invention is illustrated further by the following specific examples showing the difiusion rate of hydrogen through specific iron, nickel and chromium alloys. In each of these examples the difiusion rate was measured with a mercury slug flow meter which was connected by a hermetically sealed connection to one end of the metal tube being tested. A thermocouple well of silica was inserted through the other end and the latter was hermetically sealed. The tube Element 304-Al1oy 3l6-A11oy 347-Alloy 0 08 max 0.10 max... 0.10 max-.. 0. l0 2 00 max 2.00 max... 2.00 max... 1 00 max... 1.00 max.-. 0 04 max 0.04max...

. 0.04max...

Molybdenum. Columbium- Iron Example 1 In this example the material treated was a 304-Alloy stainless steel tube having a Wall thickness of 0.9 mm. (0.036"). The hydrogen loss as indicated is cubic centimeters of hydrogen at room temperature per square centimeter of surface per hour.

H-loss T m er Hours heated cc./cm. /hr. tu s? 1 Example 2 In this example, after heating the 304-Alloy stainless steel tube for 78 hours, the tube was cooled to room temperature, the hydrogen pumped out and air admitted for thirty minutes. It was then evacuated, filled with hydrogen and heated at 800 C. The difiusion rate now was 0.0434 cc./cm. /hr. The hydrogen in the tube then was replaced by air and the tube heated about minutes at 800 C. The air in the tube then was replaced by hydrogen and the tube heated at 800 C. for about twenty hours and the diffusion rate was 0.0650 cc./cm. /hr.

Example 3 In this example, a 3l6-Alloy stainless steel tube was treated. The hydrogen loss is given as cubic centimeters of hydrogen at room tempera Nichrome ture per square centimeter of surface per hour per millimeter of thickness.

H-loss Tempera- Hours heated ccJcmJl mm./hr. o

Ewample 4 In this example, a 347 -A11oy stainless steel tube was treated. The hydrogen loss is given in the same terms indicated in Example 3.

13-1055 7 7 Hours heated gig fgp era Example 5 In this example, a Nichrome tube was treated. The hydrogen loss is given in the same terms indicated in Examples 3: and 4.

Q 7 H-loss I Tempera- Hours heated tum, a

heating the steel in an atmosphere consisting essentially of hydrogen at a temperature not less than about 600 C. for a period of time not less than about 24 hours.

3. The method for reducing the permeability of an alloy by hydrogen which comprises heating the alloy in an atmosphere consisting essentially of hydrogen at a temperature not less than about 600 C. for a period of time not less than 24 hours, said alloy comprising iron, nickel, chromium and not more than about 0.10 per cent carbon.

4. The method for reducing the permeability of an alloy by hydrogen which comprises heating the alloy in an atmosphere consisting essentially of hydrogen at a temperature not less than about 600 C. for a period of time not less than 24 hours, said alloy comprising iron, nickel, chromium and not more than about one per cent columbium.

5. The method for reducing the permeability of an alloy by hydrogen which comprises heating the alloy in an atmosphere consisting essentially of hydrogen at a temperature not less than about 600 C. for a period of time not less than 24 hours, said alloy comprising iron, nickel, chromium and between about 1.75 to 2.50 per cent molybdenum.

References Cited in the file of this patent UNITED STATES PATENTS Heat Treatment of Stainless Steels, page 13, published by Rustless Iron and Steel Corp, Baltimore, Md. 

1. THE METHOD FOR REDUCING THE PERMEABILITY OF AN ALLOY BY HYDROGEN WHICH COMPRISES HEATING THE ALLOY IN AN ATMOSPHERE CONSISTING ESSENTIALLY OF HYDROGEN AT A TEMPERATURE NOT LESS THAN ABOUT 600* C. FOR A PERIOD OF TIME NOT LESS THAN ABOUT 24 HOURS, SAID ALLOY COMPRISING IRON, NICKEL AND CHROMIUM. 